A rapid anterograde axonal transport of carboxypeptidase H in rat sciatic nerves

Using the highly sensitive HPLC-fluorophotometry technique, anterograde and retrograde axonal transport of carboxypeptidase H (CPH), a putative prohormone processing enzyme that removes a basic amino acid from the C-terminus of a precursor peptide, was measured 12-72 h after double ligations of rat sciatic nerves. CPH-like activity in rat sciatic nerves was 60-fold lower than that in the pituitary gland. CPH-like enzyme activity was rapidly accumulated in the proximal segment and peaked 48 h after ligation. The axonal flow was 100 mm/day, indicating that CPH in rat sciatic nerves is rapidly transported to the nerve terminals as an active form. The properties of the enzyme were similar to those of CPH in the brain: The pH optimum is at 5.5, and the molecular mass is approximately 5 kDa. These results suggest that active CPH in the PNS is transported by a rapid anterograde axonal flow and may play a role in converting proneuropeptides to active neuropeptides under the axonal transport.